An aspect of carbon sequestration is the prevention of carbon dioxide emission into the atmosphere and the improved retention of carbon in terrestrial ecosystems. Combustion of fossil fuel, such as for power generation, transport, industry and domestic use, is a major factor in increasing the concentration of carbon dioxide in the atmosphere. Consequently, elevated levels of carbon dioxide can be detrimental to the environment, causing, for instance, global warming and fluctuations in global climates. For this reason, stabilizing and reducing the concentration of gaseous carbon, such as CO2, is a necessary step in diminishing the effects of warming trends, while simultaneously extending the time period within which technologies for mitigating CO2 emissions can be further developed.
One way to uncouple fossil fuel usage and CO2 levels is to improve the storage of carbon within terrestrial biomass. In this respect, plants and other worldwide vegetation are natural CO2 “sinks” that continually remove and trap gaseous carbon from the atmosphere by processes such as photosynthesis. On a global scale, plants represent an enormous quantity of stored carbon. Taken collectively, the terrestrial biosphere is estimated to sequester approximately 2 gigatonnes of carbon (GtC) per year. Of that biomass, the most abundant component of terrestrial plant materials are cellulose and lignin, which represent key carbon stores. Lignin is a very complex, aromatic macromolecule, used to form plant cell walls and structural tissues. The molecule imparts strength to the plant, facilitates water transport and impedes biodegradation of plant polysaccharides and protects plants against microbial attack. Plants that have a high lignin content, may, therefore, store a substantial amount of carbon while simultaneously being very difficult to degrade.
Nevertheless, when plant litter becomes incorporated into soil and components such as lignin are eventually broken down, the once-trapped carbon can be liberated by any number of degradative factors, especially by microbes and biochemical processes, such as oxidation. In fact, oxidation of terrestrial soil carbon is estimated to release approximately 0.5 billion tonnes into the atmosphere. Cultivation, for instance, exposes fresh soil to the air, increasing the rate of carbon dioxide emission.
Furthermore, fungi such as white-rot fungi and wood-rotting fungi, as well as a variety of bacterial and actinomycetes species, appear to be the most efficient lignin-degraders present in terrestrial ecosystems. For instance, white-rot fungi produce “lignase” peroxidase enzymes that produce free oxygen radicals that are potent lignin decomposers. Thus, a major cause of CO2 release from soil organic materials is the increased accessibility of carbon to elements that are capable of converting one form of carbon into another.
Accordingly, the rate at which carbon dioxide is produced depends upon both the surrounding environmental conditions and upon the ease by which plant materials can be broken down. Thus, the decomposability of soil organic matter reflects the nature of its chemical components. In this regard, some plant detritus and microbial biomass have a relatively short turnover time, generally less than 10 years. In contrast, soil organic carbon is more resistant to microbial degradation and takes between 10 and 100 years to break down. Since approximately 75% of terrestrial carbon is stored within soil organic material, the adaptation of soil to better retain that carbon is one focus of recent sequestration efforts.
For these reasons, there have been efforts to modify terrestrial vegetation, soil and plant-derived organic matter, so that the sequestered carbon is more difficult to access, utilize and, thus liberate.
To this end, “no-till” practices have been adopted to reduce the exposure of “fresh” soil to oxidative processes. Another is the transportation of natural organic matter to deep groundwater systems where the residence time of such materials is hundreds, if not thousands, of years. However, this latter method relies upon heavy rainfall or other similarly intense precipitation after prolonged dry periods, to wash organically-stored carbon into underground sites. Planting new trees and forest fertilization are other methods by which the terrestrial biosphere is being adapted so as to improve carbon sequestration.
There is still a need, however, for better methods of retaining carbon in soil, such as by actually modifying the terrestrial organic material that eventually becomes soil. For instance, a key query is whether the formation of “highly-recalcitrant organic macromolecules” can be enhanced through “solid amendments, microbial manipulation, or genetic selection of biomass.” See Chapter 4 of CARBON SEQUESTRATION RESEARCH AND DEVELOPMENT, December 1999 Report, U.S. Department of Energy, available at http://www.fe.doe.gov/coal_power/sequestration/reports/rd/. With regard to the latter, efforts have focused on genetic manipulation of plants. Research is being conducted on modifying the genes of perennial plants to provide resistance to microbial degradation. See 4-19 of CARBON SEQUESTRATION RESEARCH AND DEVELOPMENT. 
Another suggested approach along these lines, involves the reintroduction of genetic stocks of plants that possess higher lignin content into the biomass so as to improve carbon sequestration and to better inhibit the ability of microorganisms to decompose soil organic material. However, recombinant genetic approaches can require substantial research and development efforts and stringent control of the gene carriers that are used to introduce and incorporate foreign genes into plant genomes.
Thus, there is a need for methods that would alter the “composition of cellular components” and increase “energy content, durability and lignin content” in order to reduce decomposition rates and to improve microbial and disease resistance. See CARBON SEQUESTRATION RESEARCH AND DEVELOPMENT, a U.S. Department of Energy Report, Office of Science, December 1999.
A recent publication by Myneni (Science, 295, 1039-1041, 2002), showed that the halogen, chlorine, is naturally-occurring in plant organic materials. Indeed, Myneni showed that “organo-Cl” compounds are “the dominant forms of [chlorine] in the organic fraction of soils, sediments and aquatic systems in humified organics of all examined plant samples.” See page 1040. He states that the naturally-occurring chlorinated derivatives of organic molecules are recalcitrant in nature to “biotic and abiotic transformations.” See page 1041.
However, Myneni, describes only naturally occurring organo-chlorinated compounds that are created only after the death and degradation of a plant and its composite biomolecules. Moreover, the chlorine is added to organic molecules by the activity of fungal and microbial enzymes after death and degradation of the plant. Furthermore, the concentration of chlorinated organic compounds in humified plant material is less than 10 mM Kg−1. The plant-derived, “organo-Cl” compound is, therefore, a normal constituent of the environment, but is nevertheless, an uncontrollable entity in the environment.
The present invention solves these problems by providing a novel and efficient method for altering the composition of cellular materials, particularly lignin content, so as to reduce the rate at which the biodegradation of soil organic materials, such as lignin, occurs, while also enhancing the antimicrobial properties of lignin degradation products.